LED modules for general lighting (LED lamps, LED luminaries etc.) are conventionally made of a single LED, or a system of LEDs that are arranged in two dimensions.
An LED is characterized by its ability to generate monochrome light at a well-defined wavelength. This characteristic is useful for many applications, but complicates the generation of white light since it by definition is constituted by a mixture of wavelengths. One way to solve this problem is to add a wavelength converting material to an LED. For example, blue LEDs have been coated with a wavelength converting material that converts some of the blue light to yellow light. Thereby a white light can be provided as a mixture of converted yellow light and unconverted blue light. However, such white LEDs have limited brightness and are thus not satisfactory for use in applications requiring high light output levels.
An alternative solution is to mix light from two or more differently colored LEDs (i.e. from a multi LED). Such a multi LED arrangement also provides for dynamic adjustment of the color appearance, simply by adjusting the relative power of the respective LED components.
One such arrangement is disclosed in JP-07015044, which also proposes to put the differently colored LED units at different heights in order to improve the light output. However, the luminance of a single LED is limited. For general lighting purposes, a large number of LEDs have to be put together, which makes the illumination device bulky. This bulkiness is a general problem for compact applications, and typically also gives rise to problems in the color appearance of the device since it makes homogenous color mixing more complicated.
Hence there is a need for improved LEDs, that provide for high brightness, compactness, and homogenous color mixing.